Pipelines are utilized throughout the world for the long-distance transportation of oil, gas, industrial chemicals and other such fluids. A pipeline is typically constructed from large steel pipe sections (40-80 feet in length and 20-48 inches in diameter) which are welded together along the pipeline route and then buried underground. However, while the pipe sections delivered to the pipeline construction site are typically straight, pipeline routes rarely follow a straight line. Rather, most pipeline routes include numerous horizontal and/or vertical curves provided to follow the contours of the earth, to detour around obstacles, or because of land ownership considerations. Efficiently bending the massive sections of pipe to allow the pipeline to follow the preselected route remains a major challenge to the pipeline construction industry.
Portable pipe bending machines have been developed which permit the bending of massive pipe sections to the desired degree of curvature at the site of installation. Because of the size of the pipes being bent, the pipe bending equipment is generally massive in nature and operated hydraulically. Examples of such hydraulically-operated pipe bending machines are disclosed in U.S. Pat. No. 5,092,150 to Cunningham, U.S. Pat. No. 3,834,210 to Clavin, et al., and U.S. Pat. No. 3,851,519 to Clavin, et al., the disclosures of which are incorporated herein by reference. The pipe section is typically inserted into the bending machine to the location desired for the bend and then clamped into place. Next, the bending force is applied to bend the pipe. Finally, the machine releases the pipe for repositioning. In many cases, the degree of curvature needed for a particular pipe section exceeds the amount which can be formed by a single bend without damaging the pipe. In such cases, a succession of laterally spaced-apart bends will be made on a single pipe section to obtain the desired curvature.
The operation of hydraulic pipe bending machines may be controlled manually by a human operator or it may be controlled by a microprocessor or other form of automatic controller. Regardless of the form of control, however, hydraulically powered mechanisms are generally used for moving the pipe section into the bending position, for clamping it in place, for applying the bending force, and then for releasing the section in preparation for the next successive bending operation. It will be readily apparent that the time required for these hydraulic mechanisms to move through their operational ranges defines the lower limit on the time necessary to perform a single bend. Increasing the operating speed of the hydraulic apparatus will thus allow a reduction in the time required for bending, thus increasing the efficiency of the bending machine.
Increasing the speed of a hydraulic cylinder is usually achieved by increasing the fluid flow rate to the cylinder or by reducing the area of the cylinder. However, increasing the flow rate generally requires increasing the size of the hydraulic pump power source. Decreasing the cylinder area requires higher fluid pressure to maintain the same output force, and achieving this higher pressure also requires increasing the size of the hydraulic pump power source. A more powerful hydraulic power source raises the initial cost of the bending machine as well as its hourly operating cost due to increased fuel usage.
It can be seen from the foregoing that a need exists for a pipe bending machine which operates faster than a conventional machine having a comparably sized power source and maximum bending force. A further need exists for equipment that is easily retrofit to existing pipe bending machines to increase their operating speed without reducing their maximum bending force. Another need exists for a method of bending a pipe which provides increased bending speed without requiring additional hydraulic power or reducing the maximum bending force.